To safeguard human health it is important to prevent health-hazardous airborne pollutants from being inhaled. A first example of health-hazardous airborne pollutants are noxious gases, such as carbon monoxide (CO), nitrogen oxide (NxOy), volatile organic compounds, sulphur dioxide (SO2), and ozone (O3). A second example of a health-hazardous airborne pollutant is inhalable particulate matter. Such inhalable particulate matter comprises fine particles (particles with an equivalent diameter between about 2.5 μm and 10 μm), and ultrafine particles (particles with an equivalent diameter between about 10 nm and about 2.5 μm). Ultrafine particles are particularly health-hazardous as they tend to deposit on, and eventually encapsulate in lung tissue.
Health-hazardous airborne pollutants originate particularly from combustion sources. Apart from the neighborhood of industrial combustion sources and other stationary combustion sources, the concentration of combustion-related health-hazardous airborne pollutants is high on or near locations where motorized traffic is present. Very high local concentrations may be encountered particularly in tunnels, at or near traffic intersections and/or in or near traffic queues under conditions of limited ventilation and/or limited wind speed. A high concentration of health-hazardous airborne pollutants may also be encountered in an enclosed space such as a room in a building or in a home, or in a cabin of a vehicle. Especially automobile drivers and passengers become readily exposed to elevated concentrations of health-hazardous airborne pollutants when outside air that is polluted by exhaust gases and/or particles is admitted into the automobile cabin. This may occur when the air handling system of the automobile operates in an outside-air-inlet mode, in which air is allowed to enter the cabin from the outside of the vehicle. It is therefore desirable to automatically switch the air handling system from an outside-air-inlet mode into recirculation mode, in response to conditions pertaining to the air outside the automobile. In recirculation mode, the intake of outside air is halted and only cabin air is recirculated through the air handling system.
A sensor system for controlling a ventilation system in a vehicle is known from U.S. Pat. No. 5,725,425. The ventilation system is arranged to operate in a recirculation mode or in an air input mode. The sensor system comprises a gas sensor element and an evaluation unit. The gas sensor element is arranged to generate an output signal based on the concentration of certain noxious gases in the air outside the vehicle. The evaluation unit is arranged to generate a signal to switch the ventilation system into the recirculation mode as soon as the rate of change of the output signal of the gas sensor element exceeds a predetermined limit. In other words, the presence of the gas sensor element in the known sensor system enables the ventilation system to be switched from an air input mode into the recirculation mode in response to conditions pertaining to the air outside the vehicle, thereby preventing health-hazardous airborne gaseous pollutants from entering the vehicle's cabin from the outside via the ventilation system.
However, as in the recirculation mode no air is allowed to enter the vehicle's cabin from the outside via the air handling system, the air quality and comfort level inside the cabin quickly deteriorate due to, for instance, the production of moisture, carbon dioxide, and/or cigarette smoke by a passenger, or the release of scents by a material in the interior of the cabin. In order to minimize the pollution level inside the cabin while maintaining safe and comfortable cabin air conditions, it is therefore also desirable to be able to automatically switch the air handling system very quickly if not immediately from recirculation mode to an outside-air-inlet mode in which, at least to some extent, air is allowed to enter the cabin from the outside. In such an outside-air-inlet mode, the air entering the cabin via the air handling system is partly composed of recirculating air and partly of outside air with an adjustable mixing ratio. In this context, an optimized mixing ratio is the outcome of a judicious compromise between adequate ventilation of the cabin with outside air, in order to rapidly remove, for instance, excess moisture, carbon dioxide, odours, cigarette smoke, etc. from the cabin, and the minimization of airborne pollutants entering the cabin from the outside via the air handling system.
In the known sensor system, the decision to switch the ventilation system between recirculation mode and outside-air-inlet mode is based on the output signal of the gas sensor element, and supported by an electronic neural network, or an electronic fuzzy logic unit.
The known sensor system has a limited functionality as it is not able to optimize the mixing ratio between recirculating air and outside air in the air flow entering the cabin via the ventilation system. Consequently, the known sensor system is not able to maintain an acceptable air quality inside an enclosed space under a large variety of circumstances.